Network Bridges, Processing, and Data Communication Hardware
Network Bridges
A bridge is used to segment a network, facilitating communication between the top three teams. Network lines pass through the three teams from the bottom (as shown in the figure). Information is transmitted only when a team from one side of the bridge sends data to a computer on the opposite side. Bridges can also connect to a modem to function with a remote local area network.
Types of Processing
Centralized Processing
Centralized processing is used in mainframes, minicomputers, and multi-user microcomputers. Links to these machines are made by dumb terminals, which are not capable of processing information independently. They are in direct contact with the central PC processor. Applications reside solely on the mainframe in centralized processing, and terminals call upon them by addressing the process and program requirements.
Distributed Processing
A distributed system is multi-user and multitasking. All programs running on a distributed system will do so on the server’s CPU, which, in computing terms, is called “time-sharing.” A distributed system shares the CPU. Each user has a computer autonomously with its own CPU where applications are run. With the advent of client/server architecture, the server CPU can run any program the user requests.
Data Communication Hardware
Data communications hardware is used to transmit data between terminals (including PCs with terminal emulation) and computers, as well as between computers. These hardware building blocks include modems, fax modems, terminal processors, and runtime processors.
Modem
To access a telephone line, a modem is required. Telephone lines were designed for oral communication, not data communication. The modem (modulator-demodulator) converts digital electrical signals from one computer to analog signals, making it possible to transmit data via telephone lines. Digital electrical signals are modulated to create sounds similar to those heard on a touch-tone phone. When analog signals reach their destination, another modem demodulates them into electrical signals compatible with the computer for processing. The procedure is reversed for communication from one computer to a terminal or another computer. A modem is always needed to connect a computer via a phone line. The modulation-demodulation process is not necessary when a microcomputer or terminal is connected directly to a network through a transmission medium such as UTP cable.
Fax Modem
The fax modem performs the same function as the regular modem, plus it has another capability that allows a PC to simulate a fax machine.
Terminal Processor/Multiplexer
A terminal processor, also known as a multiplexer, is an extension of the front-end processor. Its name derives from its physical location relative to the host processor. The terminal processor collects data from several low-speed devices, such as terminals and printers, in series. It then concentrates and sends the data through a single communication channel to the front-end processor. In turn, the terminal processor receives and redistributes the output of the host to the appropriate remote terminal.